Oil-in-water and water-in-oil emulsions are widely used in the personal care and cosmetic industry to deliver ingredients to skin and hair, either by direct application thereto of milks, lotions or creams, or through the medium of wet wipes and other similar applicators.
Personal care emulsion products such as creams and milks desirably have a number of properties in combination: stability in manufacture, formulation, storage and use; a viscosity appropriate to the end use; and preferably a desirable body and good skin feel. Body and skin feel are usually assessed subjectively, and although good body and/or skin feel are commonly associated with a non-Newtonian, shear thinning viscosity profile, a shear thinning profile does not guarantee a good body or skin feel.
Emulsions also find a wider use in other applications such as industrial, e.g. in explosives, and household applications such as polishes, for example shoe polish and furniture polish, and car (or other vehicle) waxes and polishes, for example car waxes and tyre shine products.
Thickeners have been used as emulsion stabilisers. The mechanism of stabilisation when such thickeners are used appears to be that the thickener modifies the rheology of the system by increasing the low shear viscosity of the emulsion sufficiently to provide a barrier to emulsion droplet coalescence, probably by limiting the movement of the droplets.
One particular type of thickener is a high molecular weight hydrophilic carboxylic acid polymer such as the polyacrylic CARBOMER type, which, in particulate powder form, has to be dispersed homogeneously within the emulsification system. It is necessary to firstly obtain a substantially homogeneous dispersion of the polymer particles in the emulsion; and secondly to maintain the stability of the emulsion. To function effectively, the polymeric particles need to be wetted thoroughly to enable the polymer chains to untangle and become dispersed or solubilised in the aqueous phase of the emulsion. These polymers tend to clump when added to the oil or even the aqueous phase of an emulsion. The surface of a clump solvates to form a tough outer layer which prevents complete wetting of the interior of the polymer particles. This can lead to excessive mixing and wet out times, grainy texture, reduced viscosity and stability, less robust gel formation, inferior skin feet including tackiness, and partly wetted agglomerates of particles with a jelly-like appearance similar to fish eyes.
Thus, there is a need for these high molecular weight hydrophilic polymers to be included in a system which enables improved incorporation into end-use emulsions or formulated products.